This invention relates generally to the field of telecommunication networks, and more particularly to a method and system for allocating bandwidth to real-time variable bit rate (rt-VBR) traffic in a telecommunications network.
Telecommunications networks have traditionally been circuit-switch networks that have transmission paths dedicated to specific users for the duration of a call and that employ continuous, fixed-bandwidth transmission. Due to growth in data traffic created by the Internet and its related technologies, however, telecommunications networks are being moved to a packet-switching transmission model. Packet-switch networks provide a large range of digital services, from data to video to basic voice telephony. Packet-switch networks can allow dynamic bandwidth and may be connectionless with no dedicated path or connection-oriented with virtual circuits and dedicated bandwidth along a predetermined path.
Asynchronous transfer mode (ATM) is a connection-oriented packet-switching technology in which information is organized into small, fixed length cells. ATM carries data asynchronously, automatically assigning data cells to available time slots on demand to provide maximum throughput. Compared with other network technologies, ATM provides large increases in maximum supported bandwidth, designed-in asynchronous traffic support, support for multiple types of traffic such as data, video, and voice transmissions on shared communication lines, and virtual networking capabilities, which increase bandwidth utilization with high quality of service and ease network administration.
ATM cells are routed through a telecommunications network at high speeds using a switching label included in the cell. The switching label has two sections that define a virtual path (VP) and a virtual channel (VC) in the network through which the cell is routed. The use of virtual paths and virtual channels allows physical bandwidth in the network to be subdivided and separately commercialized.
Because of the low latency and predictability throughput ATM offers, it is capable of providing quality of service (QoS) features. QoS is defined in terms of the attributes of end-to-end ATM connections and is important in an integrated service network, particularly for delay-sensitive and/or loss sensitive applications such as audio and video transmissions, as well as voice-over IP. Other applications in which QoS may be important include traditional data communications, imaging, full-motion video, and multimedia, as well as voice.
Performance criteria for describing QoS for a particular connection include cell loss rate (CLR), cell transfer delay (CTD), and cell delay variation (CDV). ATM traffic is classified as either constant bit rate (CBR) traffic, real-time variable bit rate (rt-VBR) traffic, non real-time variable bit rate (nrt-VBR) traffic, available bit rate (ABR) traffic, and unspecified bit rate (UBR) traffic depending on the QoS parameters applied to the traffic. CBR and rt-VBR traffic visualize dedicated bandwidth and are intended for real time applications. ABR and nrt-VBR traffic is intended for non-real time applications which can control, on demand, their transmission rate in a certain range. Like ASR, UBR traffic is intended for non-real time applications which do not have any constraints on the cell delay and cell delay variations.
For rt-VBR which is used for voice, video, and image data, traffic parameters include peak cell rate (CPR), cell delay variation tolerance (CDVT), sustained cell rate (SCR) which is the average cell rate over time, and maximum burst size (MBS). To insure QoS for rt-VBR connections while minimizing resource over-allocation, rt-VBR traffic is statistically multiplexed together and allocated a fixed bandwidth based on the Markovian modulated Poisson, Markovian fluid flow, batch Poisson and other similar models. These models, however, are complex and thus difficult to implement in an operating environment. In addition, the models are artificial and therefore can result in both over and under allocation of resources.
The present invention provides an improved method and system for allocating bandwidth to real-time variable bit rate (rt-VBR) traffic in an asynchronous transport mode (ATM) telecommunications network that substantially eliminates or reduces disadvantages and problems associated with previous systems and methods. In particular, bandwidth is allocated to rt-VBR traffic at an egress port or link based on a probabilistic method that achieves statistical multiplexing gain and high bandwidth utilization.
In accordance with one embodiment of the present invention, a method for allocating transmission bandwidth to a group of real-time variable bit rate connections includes determining an acceptable cell loss probability for a real-time variable bit rate group based on quality of service requirements for real-time variable bit rate connections in the real-time variable bit rate group. An allocation bandwidth is determined for the real-time variable bit rate group from a probability density function of an aggregate cell arrival rate for the real-time variable bit rate group. The allocation bandwidth is the bandwidth that the probability of the aggregate cell arrival rate exceeding the bandwidth is less than or at least substantially equal to the acceptable cell loss probability.
More specifically, in accordance with a particular embodiment of the present invention, the allocation bandwidth is allocated at a network element for transmission of the real-time variable bit rate connections on an egress link. In another embodiment, the real-time variable bit rate group includes a requested real-time variable bit rate connection. In this embodiment, the network element accepts the requested real-time variable bit rate connection and allocates the allocation bandwidth in response to determining the allocation bandwidth is available for allocation at the network element. The allocation bandwidth is preferably a minimum bandwidth at which the probability of the aggregate cell arrival rate exceeding the bandwidth is less than or equal to the acceptable cell loss probability.
Technical advantages of the present invention include providing an improved method and system for allocating bandwidth to rt-VBR and other suitable types of dynamic traffic in a telecommunications network. In particular, bandwidth is allocated to rt-VBR traffic using a probabilistic method based on traffic parameters. Accordingly, under or over allocation is minimized while achieving required cell loss ratio and guaranteed cell delay parameters. In addition, the method is general for various actual cell arrival processes. This is accomplished by using a worst case scenario for cell arrival models such that no further cell arrival characterizations are necessary. The method conforms to standardized traffic descriptors and can be simplified for efficient operation within an ATM node.
Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, description, and claims.